This invention relates to a hydraulic brake system for automotive vehicles with an anti-skid device which comprises closing valves connected in each brake circuit between the master cylinder and the wheel brake cylinders and opening valves connected between the return reservoir and the wheel brake cylinders. The valves are actuated in such a manner by an anti-skid control circuit acted upon by wheel sensors as to ensure that a wheel slip occuring during braking will be prevented at one of the wheel axles, preferably at the rear wheel axle. A hydraulic level adjustment system is provided which has hydraulic lifters at the applicable wheel axle, at least one pressure source, a pressure line leading from the pressure source to the axle concerned, at least one level adjustment opening valve in the pressure line and one level adjustment closing valve at the pressure line. The valves are alternatively opened by a level adjustment control circuit as a function of and in response to level control signals emitted by level sensors.
Level adjustment in automotive vehicles generally is provided at the rear axle so as to keep the vehicle level at the same elevation for different loadings. Generally, such level adjustment systems are connected to a hydropneumatic pressure accumulator kept in a charged condition by means of a hydraulic pump. If too low a level of the vehicle body is indicated by a level sensor, the lever adjustment opening valve will be opened and pressure will be transmitted from the hydropneumatic pressure accumulator to the hydraulic lifters whereby the nominal level will be re-established. If the level of the vehicle body is too high, a level adjustment opening valve will ensure the return of hydraulic fluid to the return reservoir.
As the level adjustment system generally is located at the rear axle of the vehicle while the components generating the hydraulic pressure are situated in the area of the engine space the expenditure for lines for the supply of the level adjustment system is considerable. This substantial expenditure is due to the fact that the respective hydraulic lines must be rated for comparatively high pressures.